The present invention relates to air-conditioning systems for automobiles and methods for controlling these systems.
A typical air-conditioning system for automobiles includes a compressor for compressing refrigerant gas. The compressor is activated by the force transmitted from an automobile engine when the temperature in the passenger compartment exceeds a predetermined value. If the compartment temperature is not greater than the predetermined value, the compressor is not activated. An electromagnetic clutch is arranged in a power transmitting path for connecting the engine with the compressor. The electromagnetic clutch is selectively excited or de-excited in relation to the compartment temperature such that the compressor is engaged or disengaged from the engine accordingly.
Activation of the compressor applies load to the engine. Thus, when the engine power is transmitted to the compressor, the engine does not respond quickly to depression, or operation, of the automobile""s accelerator. Low-power engines are particularly affected by the load applied by the compressor. The response to the operation of the accelerator is significantly delayed for low-power engines.
To solve this problem, the following control procedure is executed when the accelerator is operated. When the accelerator is operated such that the throttle valve opens wider than a predetermined position, the clutch is disengaged in order to disconnect the compressor from the engine. The disengagement of the compressor from the engine removes the load applied to the engine by the compressor when the automobile is accelerated. The engine power is thus maximally transmitted to the automobile""s driving wheels.
However, since the disengagement of the clutch stops the compressor, the automobile compartment is no longer air-conditioned. Thus, the automobile driver must choose between acceleration performance and air-conditioning. In other words, the automobile cannot be smoothly accelerated while the passenger compartment is being air-conditioned. In addition, once the clutch is disengaged to enable smooth acceleration, an impact is caused when the clutch is re-engaged after completing the acceleration.
Furthermore, the predetermined throttle valve position for determining whether to disengage the clutch is selected according to traveling speed that is assumed to correspond to the predetermined throttle valve position. Specifically, as long as the traveling speed remains lower than the assumed speed, the clutch remains engaged. However, when the vehicle speed reaches the assumed speed, the throttle valve opening reaches the predetermined position, and the compressor is disengaged from the engine. That is, since the predetermined throttle valve position is constant regardless of the traveling speed, the clutch is disengaged if the accelerator is operated even by a small amount as long as the speed is greater than the assumed speed. If the clutch is disengaged, the compartment is no longer air-conditioned. Furthermore, if the depression amount of the accelerator varies in the vicinity of the reference value, the clutch is engaged and disengaged repeatedly.
Accordingly, it is an objective of the present invention to provide an air-conditioning system for automobiles and a method for controlling this system that is capable of continuing air-conditioning operation while allowing the vehicle to accelerate smoothly without hindrance.
To achieve the foregoing and other objective and in accordance with the purpose of the present invention, an air conditioning apparatus having a first sensor for detecting the position of an accelerator and a compressor. The accelerator position is defined by the degree of the depression of the accelerator. The compressor is driven by an engine of a vehicle. A displacement of the compressor is varied by an external controller. The apparatus includes a second sensor for detecting the vehicle speed, computing means and control means. The computing means computes a reference value of the accelerator position based on the vehicle speed. The reference value is used to determine that load applied to the engine by the compressor is to be decreased. The control means controls the compressor so as to decrease its displacement based on the reference value.
In another aspect of the present invention, a method for controlling air conditioning apparatus having a compressor actuated by an engine of a vehicle is provided. A displacement of the compressor is varied by an external controller. The method includes steps of: determining a driver""s attempt to decreasing load applied to the engine by the compressor based on the vehicle speed and a position of the accelerator, decreasing the displacement of the compressor after the determining step.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.